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Cash Equivalents And Restricted Cash And Securities (Summary Of Cash Equivalents And Restricted Securities) (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Mar. 31, 2018
Dec. 31, 2017
Cash and Cash Equivalents [Line Items]        
Cash Equivalents, Cost Basis $ 41,075 $ 42,236 $ 27,392 $ 40,753
Restricted Securities, Cost Basis 731 747    
Money Market Funds [Member]        
Cash and Cash Equivalents [Line Items]        
Cash Equivalents, Cost Basis 1,450 1,445    
Restricted Securities, Cost Basis 731 747    
Unrealized Holding Gains    
Cash Equivalents, Estimated Market Value 1,450 1,445    
Restricted Securities, Estimated Market Value $ 731 $ 747